1. Field of the Invention
This invention relates to the shutter speed control of a camera, and in particular to a device for synchronously controlling the exposure time of a film and the light emission of an electronic flash device.
2. Related Background Art
When flash photography is to be effected with a camera having a focal plane shutter and an electronic flash device combined together, the shutter speed of the camera must coincide with a maximum speed synchronizable to the light emission of the flash device (synchro speed) or must be set to a speed lower than that. So, a camera provided with a shutter control device for forcibly changing over the shutter speed set on the camera side to the synchro speed or lower when said shutter speed is higher than the synchro speed, at a point of time whereat an electronic flash device is mounted on the camera and a power source switch is closed or the charging of the main capacitor of the electronic flash device is completed, is well known.
As the synchro device of a focal plane shutter camera, there are aperture opening blade synchro control in which the electronic flash device is caused to emit light in synchronism with the completion of the movement of the aperture opening blades of the shutter, and aperture closing blade synchro control in which the electronic flash device is caused to emit light in synchronism with the start of the movement of the aperture closing blades of the shutter.
In the aperture opening blade synchro control, a main object is illuminated at the first moment of the exposure of a film and therefore, when an object fast in movement is flash-photographed at a relatively low shutter speed, a flow of image occurs forwardly of the object, and this leads to the disadvantage that an unnatural photograph is taken. In contrast, in the aperture closing blade synchro control, the main object is illuminated at the last moment of the exposure of the film and therefore, effective photographing becomes possible. There is also a camera provided with aperture opening blade synchro control and aperture closing blade synchro control and capable of selectively them over.
A camera provided with a plurality of different modes with respect to exposure control is also known. A camera is also known in which the shutter speed is automatically controlled so as not to be lower than a predetermined shutter speed (e.g. 1/60 sec.) in order to prevent an unsatisfactory photograph from being taken due to camera shake when a programmed automatic exposure control mode (a combination of the shutter speed and the aperture value being automatically set in conformity with the luminance of an object) or an aperture priority automatic exposure control mode is selected as the photographing mode.
However, if in flash photography, only shutter speeds always higher than 1/60 sec. are obtained, it will limit the intention of the operator who intends to obtain effective photographs. Particularly, even if the operator wants to compose the after image of a moving object in a photograph by the aperture closing blade synchro control, the operator cannot display a sufficient effect. Therefore, the operator must change over the photographing mode of the camera, for example, to a shutter priority automatic exposure control mode or a manual mode (the shutter speed and the aperture in use being manually set) each time.